CNN has a clear and frank essay on the natural and social aspects of the recent earthquakes:

About six weeks ago, a large earthquake devastated Haiti and killed over 200,000 people. Saturday, a huge earthquake releasing 500 times more energy, devastated Chile and killed hundreds.

So why did the smaller earthquake kill so many more people? And why the sudden spate of disastrous earthquakes in the Americas?

No, the apocalypse is not coming. No, the two earthquakes are not linked in any way. And no, Pat Robertson, you can't blame the Devil or the French. The real answers, for those comfortable with science and the Enlightenment, are tectonics and poverty.

...Poverty is what ultimately kills most people during an earthquake. Poverty means that little or no evaluation is made of seismic risk in constructing buildings and no zoning takes place. It means that building codes are not written, and even if they do exist they are difficult, or impossible, to enforce. It means the choice between building robustly or building cheaply is not a choice at all.

Haiti is a tragic illustration of this. Weak building materials and poor construction standards share much of the blame for the grotesque numbers of fatalities, injured and internally displaced people.

The lesson in all of this? The social is as real as the natural.